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Tag Archives: Los Molles Formation

Isaberrysaura mollensis gen. et sp. nov. is the first dinosaur recovered in the marine-deltaic deposits of the Los Molles Formation (Neuquén Province, Argentina), and the first neornithischian dinosaur known from the Jurassic of South America. So far, the South American record of Jurassic ornithischian dinosaurs was limited to a few specimens belonging to Heterodontosauriformes, a clade of small-sized forms that survived in Europe up to the Early Cretaceous. The name Isaberrysaura is derived from “Isa Berry” (Isabel Valdivia Berry, who reported the initial finding) and the Greek word “saura” (lizard).

The holotype of Isaberrysaura is an incomplete articulated skeleton with an almost complete skull, and a partial postcranium consisting of 6 cervical vertebrae, 15 dorsal vertebrae, a sacrum with a partial ilium and an apparently complete pubis, 9 caudal vertebrae, part of a scapula, ribs, and unidentifiable fragments. One of the most notable features of the discovery is the presence of permineralized seeds in the middle-posterior part of the thoracic cavity. The seeds were assigned to the Cycadales (Zamiineae) on the basis of a well-defined coronula in the micropylar region. The findings suggest the hypothesis of interactions (endozoochory) between cycads and dinosaurs, especially in the dispersion of seeds.

The cranium of Isaberrysaura is reminiscent of that of the thyreophorans. The skull is estimated to be 52 cm long and 20 cm wide across the orbits. The jugal is triradiate and the nasals are ~20 cm long. There are two supraorbital bones; one is elongated (~10 cm), as in stegosaurs, and the other element interpreted as a posterior supraorbital is located on the posterior margin of the orbit. It has at least six premaxillary teeth, and there is no diastema between the premaxillary and the maxillary tooth row. Despite the many similarities between Isaberrysaura and the thyreophorans, the phylogenetic analysis indicates that Isaberrysaura is a basal ornithopod, suggesting that both Thyreophora and neornithischians could have achieved significant convergent features.